A wind turbine is an energy conversion system which converts kinetic wind energy into electrical energy for utility power grids. Specifically, wind incident on blades of the wind turbine generator (WTG) causes a rotor of the WTG to rotate. The mechanical energy of the rotating rotor in turn is converted into electrical energy by an electrical generator. One type of wind turbine that provides constant frequency electrical power is a fixed-speed wind turbine. This type of wind turbine requires a generator rotor that rotates at a constant speed. Another type of wind turbine is a variable speed wind turbine. This type of wind turbine allows the generator to rotate at variable speeds to accommodate for fluctuating wind speeds.
A full scale power converter based wind turbine (which is a type of variable speed wind turbine) usually includes a power converter having a generator side converter coupled to a grid side converter via a direct current (DC) link. The generator side converter regulates the power of the generator. This power passes through the DC-link, and is eventually fed to the grid through the grid side converter and other power components. The grid side converter regulates the grid side power. The same is true for the Doubly Fed Induction Generator (DFIG) systems where only a portion of the power from the generator may pass through the power converter.
A wind turbine may be requested to shut down, for example due to an extreme fault in the grid, component failure in the turbine/wind farm or requested by the grid operator. A power dissipating unit is usually applied to the generator windings to dissipate the power from the generator during shut down. This ensures that when there is a sudden loss of power, there is no significant change in the shaft torque.
The activation of the dissipating unit to dissipate power from the generator is usually controlled by power switches and control circuits. In order for the wind turbine to shut down properly and safely, it is crucial that the dissipating unit, the associated switches and the control circuits are reliable. If any one of the components is faulty, it should be easily detectable in order to ensure that the drive train health is not compromised.
Hence it is desirable to provide a power dissipating arrangement which has a higher reliability compared to the existing state of the art.